Interatomic force constants and lattice vibrations of AlP,AlAs and AlSb

The interatomic force constants and the phonon dispersion curves of AlP, AlAs, and AlSb are obtained from the electronic theory of solids by using our presented binding force, which includes mainly covalent interactions in the pseudopotential formalism and partially ionic interactions. The potential-parameter, effective ionic charge and ionic fraction of AlP and AlAs are estimated from those of AlSb and other III–V tetrahedrally- bonded compounds in spite of no experimental information on the band- calculation and the neutron scattering data of AlP and AlAs. Numerical data for the crystal energy of AlP and AlAs are in good agreement with the observed data, and the obtained results for the phonon dispersion curves and bulk modulus are useful to study the lattice dynamics and anharmonic properties of these compounds.     

A simple model for the surface energy of ionic crystals

The surface energy of ionic materials is empirically related to bulk properties (elastic constants, electronic dielectric constant and optical band gap) through an analysis of the cleavage force. This is evaluated at small and large separations of the two crystal halves from phonon dispersion curves and from van der Waals interactions, respectively, and these two limiting behaviours are connected by a scaling hypothesis introduced for metals by Kohn and Yaniv. The experimental data that are available for a few ionic crystals seem to satisfy the suggested relation, with an empirical universal parameter which has roughly the same value as determined for metals.     

LO声子色散对激子结合能的影响

本文计及纵光学声子的色散,计算了激子的结合能,发现计及声子色散所导出的激子有效势,对计算激子的结合能有所改进.     

极化子在正弦色散声子场中的性质

本文计及纵光学声子的色散,在正弦近似下,用微扰法了多原子晶体中极化子的基态能量,有效质量和自能。     

The interaction of optical phonons with magnetoplasma waves in ionic semiconductors

The interaction of magnetoplasma waves with optical phonons is investigated for propagation both parallel and perpendicular to the external de magnetic field. The low frequency region is considered where helicons and Alfvén waves propagate for uncompensated and compensated materials, respectively. The results are applied to degenerate, ionic semiconductors where the plasma frequency is much larger than the infrared dispersion frequency and the cyclotron frequency. The theory is applied to heavily-doped InSb for the case of helicon-optical phonon interactions.     

Nonlinear optical responses due to exciton-phonon interactions in strongly coupled exciton-phonon systems

The excitonic nonlinear optical responses due to exciton-phonon interactions in strongly coupled exciton-phonon systems are investigated theoretically. It is shown that the influence of exciton-phonon interactions on the nonlinear optical absorptions and Kerr nonlinear coefficients is significant as the signal field frequency detuning from the exciton frequency approaches to the optical phonon frequency. How to manipulate the nonlinear optical responses by using the control fields is also presented.Received: 16 March 2004, Published online: 4 May 2004PACS: 42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption - 42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift - 42.25.Bs Wave propagation, transmission and absorption - 72.80.Le Polymers; organic compounds (including organic semiconductors)     

Polaron self-energy and effective mass in a freestanding cylindrical quantum wire

The polaron self-energy and correction to the electron effective mass in a freestanding quantum wire is investigated by the perturbation approach.The polaron effect of the electron-confined longitudinal optical (LO) phonon and surface optical (SO) phonon interactions are separately worked out. Numerical calculation on a GaAs quantum wire shows that the confined LO phonon contribution to the polaron self-energy is relatively small for a narrow wire and gradually approach that of the bulk material when the radius of the wire increases. While the contribution of the SO phonon modes is big for small wire radius and then decreases as the radius increases.     

Effective ionic charges in CdGa2Se4 and CdGa2S4

Available experimental data (Raman and Infrared) on the optic phonon spectra in defect chalcopyrite crystals CdGa₂Se₄ and CdGa₂S₄ are used to determine the dynamical ionic effective charges. The results are compared with those found in other ternary compounds as spinels and chalcopyrites. An emperical correlation between the normalized Szigeti charges and the optical dielectric constant is discussed.     

Effects of electric field and size on the electron-phonon interaction in a spherical quantum dot with impurity

The effects of electric field and size on the electron-phonon interaction with an on-center impurity in a Zn_1?x Cd _x Se/ZnSe spherical quantum dot are studied, taking into account the interactions with confined, half-space and surface optical phonons. In addition, the interaction between impurity and phonons has also been considered. The results show that the electron-confined, electron-half-space, and electron-surface optical phonon interaction energies are all negative. The electron-confined optical phonon interaction energy is weakened by the electric field, but the electron-half-space and electron-surface optical phonon interaction energies are strengthened by it. In particular, the electron-surface optical phonon interaction depends strongly on the electric field, and it will vanish when the electric field is absent. It is also found that the electron-confined optical phonon interaction and electron-impurity “exchange” interaction energies reach a peak values as the quantum dot radius increases and then gradually decrease, but the electron-half-space optical phonon interaction energy exponentially quickly approaches 0 as the quantum dot radius increases.     

Phonon properties of rare earth ytterbium pnictides

We report for the first time the complete phonon dispersion curves for the ytterbium pnictide compounds (YbN, YbP and YbAs) using a breathing shell model to establish their predominant ionic nature. The calculated results also show that this group of rare earth compounds does not show any elastic and phonon anomalies which are the characteristic features of other rare earth compounds. We emphasize the need for further Raman and neutron scattering measurements.     

极化子效应对ZnS/CdSe核壳量子点光吸收系数的影响

在有效质量近似下,利用量子力学密度矩阵理论,从理论上研究了考虑极化子效应后核壳量子点中线性、三阶非线性以及总的光吸收系数在不同条件下随入射光能量变化的关系。通过数值计算,分析了电子-LO声子和电子-IO声子相互作用对ZnS/CdSe柱型核壳结构量子点光吸收系数的影响。结果表明,极化子效应对光吸收系数有很大影响,不同声子模式对光吸收系数影响大小不同。考虑电子-LO声子后,光吸收系数被大大提高。另外,入射光强和弛豫时间对系统的吸收系数也有很大影响。     

Ternary mixed crystal effects on interface optical phonon and electron-phonon coupling in zinc-blende GaN/AlxGa1−xN spherical quantum dots

The theoretical investigations of the interface optical phonons, electron–phonon couplings and its ternary mixed effects in zinc-blende spherical quantum dots are obtained by using the dielectric continuum model and modified random-element isodisplacement model. The features of dispersion curves, electron–phonon coupling strengths, and its ternary mixed effects for interface optical phonons in a single zinc-blende GaN/Al_xGa_1−xN spherical quantum dot are calculated and discussed in detail. The numerical results show that there are three branches of interface optical phonons. One branch exists in low frequency region; another two branches exist in high frequency region. The interface optical phonons with small quantum number l have more important contributions to the electron–phonon interactions. It is also found that ternary mixed effects have important influences on the interface optical phonon properties in a single zinc-blende GaN/Al_xGa_1−xN quantum dot. With the increase of Al component, the interface optical phonon frequencies appear linear changes, and the electron–phonon coupling strengths appear non-linear changes in high frequency region. But in low frequency region, the frequencies appear non-linear changes, and the electron–phonon coupling strengths appear linear changes.     

Influence of spin–orbit interactions on the polaron properties in wurtzite semiconductor quantum well

We have study the simultaneous effect of Rashba and Dresselhaus spin–orbit interactions on the polaron properties in wurtzite semiconductor quantum wells. The linear and cubic contributions of the bulk Dresselhaus spin–orbit coupling and the effects of phonon confinement on electron–optical-phonon interaction Hamiltonians are taken into account. We have found analytical solutions for the polaron energies as well as polaron effective mass within the range of validity of perturbation theory. It is shown that the polaron energy and effective mass correction are both significantly enhanced by the spin–orbit coupling. Wave number dependent phonon contribution on the electron energy has minima and varies differently of the spin-up and spin-down states. Polaron self-energy due to interface optical phonon modes has larger values than of the confined optical phonon modes ones. The polaron effective mass exhibits anisotropy and the contribution of the Dresselhaus spin–orbit coupling term on the polaron effective mass is dominated by Rashba one.     

多原子半无限晶体中表面极化子的内部激发态

研究多原子半无限晶体中电子与表面光学(SO)声子耦合强,而与体纵光学(LO)声子耦合弱的极化子的激发态性质.采用线性组合算符和幺正变换方法导出与SO声子耦合强而与LO声子耦合弱情形下极化子的基态能量、第一内部激发态能量和激发能量.结果表明,多原子半无限晶体中与SO声子耦合强,而与LO声子耦合弱的极化子的基态能量、第一内部激发态能量不仅包含不同支LO声子和不同支SO声子与电子耦合的能量,而且也包含不同支SO声子之间相互作用贡献的附加能量.激发能量与体纵光学声子无关.     

Effect of electron-phonon interaction on surface states in zinc-blende GaN,AlN, and InN under pressure

A variational approach is used to study the surface states of electrons in a semi-infinite polar semiconductor under hydrostatic pressure. The effective Hamiltonian and the surface-state levels are derived including the effects of electron-optical phonon interaction and pressure. The numerical computation has been performed for the surface-state energies versus pressure for zinc-blende GaN, AlN, and InN. The results show that the effect of electron-optical phonon interaction lowers the surface-state energy. It is also found that the effect of electron-surface optical phonon interaction is much bigger than the effect of electron-half space longitudinal optical phonon interaction for surface-state levels. It indicates that the surface-state energies and the influence of electron-phonon interaction increase with pressure obviously.Received: 12 June 2003, Published online: 22 September 2003PACS: 63.20.Kr Phonon electron and phonon-phonon interactions - 71.38.-k Polarons and electron-phonon interactions - 73.20.At Surface states, band structure, electron density of states     

Lattice dynamics and ionic charge of VI2

We present an Extended Shell Model calculation of the phonon dispersion curves in VI₂. The dynamical matrix is derived from interionic potentials including Coulomb monopole and dipole, van der Waals, nearest-neighbor and next-nearest-neighbor Born-Mayer repulsive interactions. The potential parameters are either known in literature or derived from lattice constants and cohesive energy. A suitable choice of only three adjustable parameters (net charge Z, shell charge and shell-core displacement) yields an excellent fit of the five optical frequencies and of the anion static dipole. The resulting ionic charge Z = 0.75 is very well consistent with the recent neutron data on transferred hyperfine interaction.     

Temperature dependence of Raman linewidth and shift in CuI

The temperature dependence of the optical phonon linewidth and frequency shift in CuI has been measured in the temperature range of 4.2 ～ 300 K. Utilizing phonon dispersion curves obtained from neutron scattering measurements, the linewidths and frequency shifts are calculated in terms of three-phonon interactions proposed by Pine and Tannenwald. The experimental results for the change in linewidth and frequency with temperature are in good agreement with this theory.     

束缚极化子有效质量的温度特性

采用改进的线性组合算符和幺正变换方法研究强、弱耦合束缚极化子的有效质量的温度特性,对RbCl晶体进行数值计算。结果表明,强耦合束缚极化子的振动频率和有效质量随温度的升高而增加,随库仑势的增加而增大。     

Ternary effects on the optical interface phonons in onion-like GaN/AlxGa1 − xN quantum dots

The interface optical phonons and its ternary effects in onion-like quantum dots are studied by using dielectric continuum model and the modified random-element isodisplacement model. The dispersion relations, the electron–phonon interactions and ternary effects on the interface optical phonons are calculated in the GaN/Al_xGa_1 − xN onion-like quantum dots. The results show that aluminium concentration has important influence on the interface optical phonons and electron–phonon interactions in GaN/Al_xGa_1 − xN onion-like quantum dots. The frequencies of interface optical phonons and electron–phonon coupling strengths change linearly with increase of aluminium concentration in high frequency range, and do not change linearly with increasing aluminium concentration in low frequency range.     

Polarons in a cylindrical quantum well wire with finite confining potential

The polaron self-energy and the correction to the electron effective mass in a cylindrical quantum well wire (QWW) are studied by the perturbation approach. The interactions of electrons with different phonon modes in the QWW system, including the confined longitudinal optical phonon modes, in the wire (LO1), in the barrier materials (LO2) and in the interface optical (IO) phonon modes, are considered. The result shows that the LO1 phonon’s contribution to the polaron self-energy increases gradually as the radius of the wire increases, and finally reaches that of the three-dimensional limit, while the LO2 phonon contributes only when the radius of the wire is very small. Also, the contribution of the IO phonon modes first increases quickly as the wire radius increases and soon reaches a maximum, then reduces to zero monotonically.